Hydraulic control device for a viscous fluid pump

ABSTRACT

In a hydraulic control device for a viscous fluid pump with at least one feed cylinder (11) drivable by a hydraulic cylinder (12), the feed chamber (17) of which can be alternately connected via a hydraulically operable inlet valve (18) a hydraulically operable outlet valve (21) to a reservoir (19) and a feed line (22), whereby in the loading phase of the feed cylinder (11) the inlet valve (18) is open and the outlet valve (21) closed and in the feed phase of the feed cylinder, in which its piston is driven so as to reduce the volume in the feed chamber (17), the outlet valve is open and the inlet valve is closed, and with a hydraulic sequence control actuating the correct cyclic changeover between the inlet and outlet valves and the changeover of the pump drive, a valve forming part of the changeover control device of the sequence control and relieving the pressure in the feed chamber of the control cylinder (53) designed to actuate the outlet valve (21) takes the form of an electrically or hydraulically actuated valve (71) controlled dependently upon the high pressure in the drive cylinder (12) of the feed cylinder (11). Said valve (71) is switched to its through-flow setting on reaching an adjustable and predeterminable minimum of the pressure in the drive cylinder (12).

FIELD OF THE INVENTION

The invention relates to a hydraulic control device for a viscous fluidpump that includes at least one feed cylinder drivable by means of ahydraulic cylinder.

BACKGROUND OF THE INVENTION

Hydraulic control devices such as are known from German Patent DocumentDE 38 33 845 A1 are used to control two-cylinder viscous fluid pumps.The feed cylinders of these pumps are each driven by a hydraulic linearcylinder, work in a push-pull operation. In other words, one cylinderfeeds, while the other--in the so-called suction stroke--is loaded withmaterial to be transported, for example with concrete. The alternatingopening of the feed chambers of the two feed cylinders toward thestorage container containing the material to be transported and thealternating connecting of the feed chambers to a feed line is done by atube switch. This switch controls both the function of an inlet valvefor the feed cylinders which, through a changeover of the tube switch,moves into a communicating connection with the storage container, andalso the function of an outlet valve for the feed cylinder carrying outthe feeding stroke, the feed chamber of which feed cylinder beingconnected to the extended feed line. To changeover the tube switch tothe two alternative feed paths, hydraulic linear cylinders acting inopposite directions are provided. The pistons of these cylinders arekinematically positively coupled with one another through the tubeswitch and can be reversed through an alternating pressure loading andpressure relief of the bottom-side control chambers of the two linearcylinders.

The feed line, which can be connected alternatingly to the feed chambersof the feed cylinder through the tube switch, can be blocked from thetube switch by means of a shutoff device controlling the function of theoutlet valve. This shutoff device is a seated valve which can be movedinto its blocking position by a bottom-side pressure loading of ahydraulic control cylinder, in which blocking position the feed line isblocked off from the tube switch. After the pressure relief of thebottom-side control chamber toward the tank of the pressure-supplyplant, this valve is moved into its open position connecting the tubeswitch to the feed line by the pressure developing during the feedingoperation in the respective feed cylinder in its feed chamber. Tocontrol the feeding operation of the viscous fluid pump, a sequencecontrol is provided which reacts to hydraulic or electrical outletsignals from the end-position indicators which monitor the positions ofthe drive cylinders of the feed cylinders, the control cylinders for thetube switch and the control cylinder of the shutoff device. Thissequence control ensures that the feed cylinders are actuated to carryout the feeding or loading stroke until after the tube switch has beenmoved into the operating position suited for the feeding and loadingoperation of the feed cylinders. The flow path, through which thepressure loading of the control cylinder in the sense of a closingmovement of the shutoff device occurs, leads through a check valve,which is loaded in an opening direction by the high control pressure.The relief path, through which pressure medium can discharge from thebottom-side drive chamber of the control cylinder, is guided through apressure-limiting valve which is connected in parallel to the checkvalve. This pressure-limiting valve is set in its open position as soonas the pressure--during the feeding operation--exceeds an adjustablepresettable value. This is supposed to occur so that the shutoff deviceopens only when the pressure in the feed chamber of the respective feedcylinder operating in the feeding operation corresponds approximately tothe pressure existing in the feed line in order to achieve a desiredpre-compression of the material being transported in the feed chamberand to avoid uneven operation of the pump caused by the pressuredifferences between the feed chamber and the feed line.

This type of changeover of the shutoff device prevents the pressure inthe bottom-side drive chamber from dropping below the pressure thresholdspecified by the setting of the pressure-limiting valve. This may not beadvantageous as long as during the course of the pump operation thefriction ratios do not change and the pre-compression pressure issufficient to open the shutoff device against the pressure present atthe shutoff device, which hereby, however, will not reach a definiteopening position but a position of a dynamic pressure balance, that is,it will stop in a position between its closing position and the positionof a maximum opening cross section. This position will be, in particularwith the common arrangement of the feed line such that it brancheslaterally off from the valve chamber through which the piston rod of thecontrol cylinder, which piston rod has the valve member, axially passes,a position in which the valve member is in the area of the port opening,which from a technical flow standpoint is much less favorable than whenthe piston can be moved on into an end position, in which the portopening of the feed line is completely open. A disadvantageous result ofthis is that a significant greater amount of driving energy is neededfor the drive cylinder of the feed cylinder; in addition, the position,in which the control piston of the shutoff device reaches its balancingposition, can also depend on the friction ratios in the drive system,with which a clear correction between the necessary pre-compressionpressure and the pressure which is indeed needed to open the shutoffdevice, does not exist so that in particular when the friction ratioschange during the course of a longer operation, an increasingly unevenrun of the pump occurs. This can indeed be countered by reducing thereaction threshold value of the pressure-limiting valve which, however,is complicated.

If, on the other hand, an "active" opening of the shutoff device isachieved, for example, by loading the rod-side drive chamber of itscontrol cylinder with pressure for opening the shutoff device, then acorrelation between the pre-compression pressure and the openingpressure of the shutoff device does no longer exist, and it is at leastdifficult to achieve an adjustment of the pump and its control valves sothat the shutoff device opens at least approximately at the pressureexisting in the feed line, which is the important condition for beingable to avoid compression strokes or decompression strokes during thechangeover of the cylinders from the feeding to the loading operation.In addition, such an active opening of the shutoff device requires asignificant amount of technical hydraulic switching and additionalexpense.

SUMMARY OF THE INVENTION

The purpose of the invention is, therefore, to improve a hydrauliccontrol device of the above-mentioned type for a viscous fluid pump sothat significantly vibration-free operation of the pump can be achieved.

This purpose is achieved according to the invention in such a mannerthat the valve of the changeover control device, which controls thepressure relief of the driving pressure chamber of the control cylinderprovided for operating the outlet valve, is designed as an electricallyor hydraulically operable valve. The valve state is a function of thehigh pressure produced for the pressure loading of the drive cylinder ofthe feed cylinder. The valve, upon reaching an adjustably preset minimumvalue of the pressure coupled into the drive cylinder, is switched intoits through-flow position, in which pressure medium can discharge fromthe driving chamber of the control cylinder.

With this type of changeover of the outlet valve, frictional effects,which could influence the opening of the valve are, so to speak,eliminated, and it is achieved in a simple manner that the outlet valveopens at a pressure in the feed chamber of the feed cylinder, whichpressure corresponds in a very good proximity with the pressure existingin the feed line which, at an optimum, corresponds with the quietoperation of the pump, with a one-time adjustment of the minimum valueof the pressure at the start of the operation being sufficient toachieve, with a specified composition of the material to be transported,the mentioned favorable operating conditions during the operation.

With the alternative designs of the pressure-relief valve, one as athrough-flow valve which, when it opens, transfers immediately into itsposition with the greatest through-flow cross section, or as aproportional valve which with an increasing control pressure releases anincreasingly greater opening cross section, with a check valve eachbeing connected in parallel to one such valve, which check valve isloaded by higher pressure at its connection remote from the changeovercylinder than in the driving pressure chamber of the control cylinder inopening direction and through relatively higher pressure in the drivingpressure chamber in blocking direction, various changeovercharacteristics can be achieved which, depending on the purpose of thepump, can be utilized in the sense of a quiet run of the pump.

In place of such a pressure-controlled through-flow valve with a checkvalve connected in parallel thereto, it is also possible according to apreferred development of the control device of the invention to providea remote-controlled check valve controlling the functions of both thethrough-flow valve and also the check valve, which remote-controlledcheck valve is blocked in blocking direction by a relatively higherpressure in the driving pressure chamber of the control cylinder andreaches its open position corresponding with the maximum opening crosssection through remote control by means of the pressure coupled into thedrive cylinder of the feed cylinder.

When the drive cylinder of the feed cylinder has a first end-positionindicator which emits an end-position signal impulse when the piston ofthe drive cylinder--in the end phase of the feeding stroke of the feedcylinder--reaches the direct vicinity of its end position in thisrespect, and has a second end-position indicator which emits anend-position signal impulse when the piston of the drive cylinder--inthe end phase of the loading stroke of the feed cylinder--reaches thedirect vicinity of its end position in this respect and an operatingcontrol valve can be switched with the end-position signal impulses ofthe end-position indicators, through which control valve occurs each ina push-pull operation the pressure loading and relief of inlet chambersof hydraulic cylinders associated with the inlet and the outlet valvesas operating elements in such a manner that the inlet valve closes ateach one of the two feed cylinders when the outlet valve opens and theclosing and opening movements of its inlet and outlet valve take placein a reverse sequence at the respective other feed cylinder, and when atleast one end-position indicator is provided, which produces an outletimpulse when the inlet valve reaches its blocking position and a furtherend-position indicator, which produces an outlet signal correlated tothe widest possible open position of the inlet valve, and the outletsignals of these end-position indicators associated with the valvepositions control the changeover of a main slide valve, which controlsthe feeding and loading phases of the feed cylinder. A further preferreddevelopment of the control device provides that the further end-positionindicator provided for detecting a valve position is associated with theoutlet valve and produces its outlet signal when the piston of thehydraulic cylinder, provided for the closing and opening control of theoutlet valve, reaches its end position connected with the blocking stateof the outlet valve. Thus a reliable sequence control of the viscousfluid pump is possible in this manner by means of the end-positionindicators which can be realized as a purely hydraulic control whenhydraulic impulse transmitters are utilized as the end-positionindicators and the valves controlled by these are designed aspressure-controlled valves, or as an electric sequence control when theend-position indicators are designed as electrical or electronicposition sensors and the valves controllable by these are designed asmagnetic valves.

The hydraulic control device is also suited for a viscous fluid pumpdesigned as a two-cylinder pump with feed cylinders, which can be drivenin a push-pull operation controlled by a changeover of the main slidevalve, and the feed chambers of which feed cylinders can be connected ina corresponding push-pull operation through an inlet valve to thestorage container and an outlet valve to a common feed line, with thepush-pull operation of the inlet and of the outlet valves, whichpush-pull operation is also controlled through the sequence control withthe push-pull control of the drive cylinders, being done by means ofhydraulic differential cylinders as changeover cylinders, through thealternative bottom- or rod-side pressure loading of which these valvescan be controlled into their closing or into their open positions, andwith the related pressure loading of these changeover cylindersoccurring through two control lines connected to an operating controlvalve, which control lines are connected in virtually "complementary"switch connections to the bottom-side control chamber of each one of thecontrol cylinders of the inlet valves and the rod-side control chamberof the respective other one of the inlet valves.

A technically simple realization of the control of the operatingsequences is possible in such a viscous fluid pump in such a manner thatoutlet signals needed for the reversal of the operating control valveare emitted by end-position impulse transmitters which are associatedwith one of the drive cylinders provided for a feed cylinder, and emit asignal when the piston of this drive cylinder reaches its end positionconnected to the end phase of the feeding stroke or the end phase of theloading stroke, and control signals needed for the changeover control ofthe main slide valve, through which occurs the drive control of thedrive cylinders of the two feed cylinders, which drive control takesplace in the sense of the push-pull operation, are produced byend-position indicators which are associated with the hydrauliccylinders provided for the changeover of the inlet valves and emit anend-position impulse always when the pistons of these hydrauliccylinders each reach the end position connected with the closed positionof the respective valve.

A changeover device advantageously provided for the two-cylinder viscousfluid pump, by means of which the pump can be switched to returnoperation, during which viscous fluid is pumped from the feed line backinto the storage container, can be realized in a simple manner such thatchangeover control devices of the outlet valves are each connectedbetween the control chambers of the changeover cylinder of the outletvalve, through the pressure loading of which this valve is switched intothe closing position, and the one of the two control lines, through thepressure loading of which the inlet valve belonging to the same feedcylinder can be controlled into its open position, and that for the twochangeover cylinders of the outlet valves there is provided anoperational changeover valve which, in a spring-centered base positionassociated with the normal feeding operation, connect the rod-sidecontrol chambers of the changeover cylinders of the outlet valves to thetank of the pressure-supply plant, and in its through-flow positionalternative thereto connects the rod-side control chambers of thechangeover cylinders of the outlet valves each to those of the twocontrol lines through which the inlet valve of the feed cylinder iscontrolled into its blocking position.

In order to assure also at comparatively low feed pressures that acycle-correct changeover of a main slide valve can occur, through whichthe alternating pressure loading and relief of the two drive cylindersof the viscous fluid pump occurs, end-position impulse signals utilizedfor its control and released with the closing of the inlet valves, withwhich end-position impulse signals the changeover parts of the mainslide valve can be operated, are fed thereto through time-delayelements.

When this main slide valve is designed as a pressure-controlled valvewhich can be switched between its alternative operating position byalternatively loading two control chambers with pressure, suchtime-delay elements can be designed as simple throttle points which arearranged in the impulse-signal paths leading from the impulsetransmitters to the control chambers of the main slide valve. It canthereby be sufficient when the mentioned time delay is active onlyduring the return operation of the viscous fluid pump and thus thethrottle points are arranged in the through-flow paths of an operationalchangeover valve, through which during the return operation theend-position pressure impulses are fed to the control chambers of themain slide valve.

It is advantageous in every case when alternatively or in addition tosuch throttle points of an operational changeover valve there areprovided throttle points of the impulse-signal path which are formed byadjustable throttles in order to adjust their flow resistances in viewof a reliable changeover of the main slide valve.

In a two-cylinder viscous fluid pump, in which for connecting therespective feeding cylinder to a common feed line and connecting theother cylinder to the storage container of the pump, there is provided aS-tube switch, the outlet side of which can be blocked against the feedline during the changeover of the drive cylinder and of the switchitself by means of a shutoff device, for the drive of which adifferential cylinder is provided, through the bottom-side pressureloading of which the shutoff device which is arranged at the end of thepiston rod of the differential cylinder, which end is remote from thepiston, can be moved into its closing position. A particularly simplerealization of the hydraulic sequence control provided for theoperationally correct control of the drive cylinder of the pump and ofthe inlet valves and of the shutoff device is possible in such a mannerthat a valve combination including a closing control valve and anopening control valve in a hydraulic series connection, which valvecombination has a first outlet which is connected to the control inletof the changeover control device, through which the pressure loading ofthe bottom-side control chamber of the differential cylinder for closingthe shutoff device and the pressure relief of this control chamber foropening the shutoff device is done, and a second outlet, which can beconnected to the rod-side control chamber of the changeover cylinder ofthe shutoff device through an operational changeover valve associatedwith the shutoff device, with the pressures at the two outlets of thevalve combination being able to be reversed by individually switchingeach one of the two closing and opening control valves.

By means of a second operational changeover valve associated with theshutoff device, in the operating position of which, which operatingposition is associated with the return operation, the high controlpressure is present at the other operational changeover valve of theshutoff device, there is also created a bypass to the inlet and theoutlet control valve of the shutoff device, through which thedifferential cylinder is permanently held during the return operation ofthe pump in the pressure-loading state corresponding with the openposition of the shutoff device.

By means of an end-position indicator, which produces an output signalcharacteristic for reaching the closing position of the shutoff device,with which outlet signal a control-pressure supply control valve can becontrolled, through which the control pressure can be fed to thechangeover cylinders of the tube switch, it is guaranteed in a simplemanner that the changeover of the tube switch and of the drive cylinderoccurs only after the shutoff device has closed. If the pump of thepressure-supply plant is designed as a load-sensing control pump, it isalso possible to control with the output signal of the end-positionindicator of the shutoff device an operating phase of the pump toachieve a maximum feed performance.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and characteristics of the invention result from thefollowing description of specific embodiments in connection with thedrawings, in which:

FIG. 1 illustrates a hydraulic schematic of a one-cylinder viscous fluidpump with a hydraulic control device of the invention,

FIG. 1a illustrates a design of a changeover control device for anoutlet valve provided within the scope of the hydraulic control device,which design is an alternative to the exemplary embodiment according toFIG. 1,

FIG. 1b illustrates an end position sensor that can be mounted to therod side of the outlet valve control chamber in order to provide asignal indicating that the outlet valve is in the fully boxed stateaccording to an alternate design of this invention,

FIG. 1c illustrates alternative placement of the operational changeovervalve for controlling the forward/reverse fluid flow of the pump of thisinvention,

FIG. 2 illustrates a hydraulic schematic of a further exemplaryembodiment of a hydraulic control device of the invention for atwo-cylinder viscous fluid pump, in which for each feed cylinder thereis provided an inlet and an outlet valve, and

FIG. 3 illustrates a hydraulic schematic of a hydraulic control deviceof the invention for a two-cylinder viscous fluid pump having a S-tubeswitch for coupling of the two feed cylinders to a common feed line.

DETAILED DESCRIPTION

A viscous fluid pump, for example a concrete pump, identified byreference number 10 and illustrated in FIG. 1 is designed as aone-cylinder pump. Pump 10 has a feed cylinder 11 which is driven bymeans of a--linear--drive cylinder 12. Cylinder 12 has a piston 13 whichis rigidly connected to the piston 16 of the feed cylinder 11 through apiston rod 14. The piston 16 of the feed cylinder 11 forms theone-sidedly movable boundary of a feed chamber 17. Chamber 17 isconnected communicatingly to a storage container 19 containing the goodsto be transported. An inlet valve 18 regulates flow between the feedchamber 17 and the storage container 19. The feed chamber 17 isconnected communicatingly to a feed line 22. An outlet valve identifiedby the reference numeral 21 controls the flow to and from the feed line22.

The drive cylinder 12 is designed as a double-acting cylinder. Cylinder12 has a bottom-side driving pressure chamber 23 and a rod-side drivingpressure chamber 24. Chambers 23 and 24 are connected alternatively to ahigh-pressure (P)-supply connection 26 and a return (T) connection of apressure-supply unit 28. Unit 28 is employed to supply pressure both tothe hydraulic circuit formed by the drive cylinder 12 and to a controlcircuit 29. Control circuit 29 controls the sequence of the opening andclosing of the inlet valve 18 and of the outlet valve 21. The return(T_(x)) connection 31 of the control circuit 29 and the returnconnection 27 of the load circuit are connected directly to the tank 32of the pressure-supply unit 28. The control pressure (P_(x)) connection33 of the control circuit 29 is connected directly to a pressure outletport 34 of a high-pressure pump 36 of the pressure-supply unit 28.High-pressure pump 36 is designed as an adjusting pump, for example asan axial piston swivel disk pump. An adjustable throttle 37 is connectedbetween a high-pressure outlet port 34 on the high-pressure pump 36 andthe high-pressure (P)-supply connection 26 of the load circuit to effecta pressure load adjustment.

A main slide valve 38 is provided to control the movement of thedrive-cylinder piston 13 and the associated feed-cylinder piston 16 soas to establish the periodic feed phases in the feed chamber 17. In theillustrated exemplary embodiment, slide valve 38 is a hydraulicallyservo-controlled 4/3-way valve. The main slide valve 38 has a "middle"base position O, in which both driving pressure chambers 23 and 24 ofthe drive cylinder 12 are relieved of pressure toward the tank 32 of thepressure-supply plant 28 and are blocked off from the high-pressuresupply connection 26. The valve 38 has a first through-flow setting Iassumed during the control pressure loading of a first control chamber39 with control pressure P_(x). When slide valve 38 is in this state,the high-pressure supply connection 26 of the load circuit is connectedto the bottom-side driving pressure chamber 23 of the drive cylinder 12.The rod-side driving pressure chamber 24 of cylinder 12 is connected tothe tank 32 of the pressure-supply unit 28. When these connections areestablished, the feed-cylinder piston 16 is driven in the sense of areduction of the volume of the feed chamber 17, namely in direction ofthe arrow 41. The valve 38 has a second through-flow setting II assumedduring loading of a second control chamber 42 with control pressureP_(x). When slide valve 38 is in this state, the bottom-side drivingpressure chamber 23 of the drive cylinder 12 is relieved of pressuretoward the tank 32 of the pressure-supply plant 28, and the rod-sidedriving pressure chamber 24 of the drive cylinder 12 is loaded with thesupply pressure accumulated at the high-pressure supply connection 26 ofthe load circuit. Consequently, the piston 16 of the feed cylinder 11 isdriven in the sense of an enlargement of the volume of the feed chamber17, namely in direction of the arrow 43.

The reversal of movement of the pistons 13 and 16 of the drive cylinder12 and of the feed cylinder 11 occurs periodically during the operationof the viscous fluid pump 10. The movement of pistons 13 and 16 ismonitored by a first hydraulic end-position indicator 44 which emits ahigh-pressure impulse when the piston 13 of the drive cylinder 12 hasreached its end position indicated in dashed lines near the feedcylinder 11, and a second hydraulic end-position impulse transmitter 46which emits a high-pressure control impulse when the piston 13 of thedrive cylinder 12 reaches its end position near the bottom. Thepressure-outlet impulses of the end-position impulse transmitters 44 and46 trigger the needed reversal of the inlet valve 18 and of the outletvalve 21. Only after these valves 18 and 21 have assumed their open orclosed position suited for the respective phase of the pump cycle,namely, the loading or the feeding phase, is the main slide valve 38reversed.

The end-position impulse transmitters 44 and 46 are pressure-controlledone-way valves which include sensor inputs 47 and 48, respectively,which can be crossed by the piston 13 of the drive cylinder and canagain be released in the respective end position of same, which sensorinput 47 or 48 can be "crossed" by the piston 13 of the drive cylinder12 and is again released in the respective end position of the piston13. Transmitters 44 and 46 further include reference inputs 49 and 51,respectively, which cannot be crossed by the piston 13. Reference input51 is attached to the bottom-side driving pressure chamber 23 and isconnected to the first end-position impulse transmitter 46. Referenceinput 49 is attached to the rod-side pressure chamber 24 and isconnected to the to transmitter 44. The end-position impulsetransmitters 44 and 46 emit at their impulse outlets 50 and 55,respectively, output pressure impulses. End-position transmitters 44 and46 only transmit pressure impulses only when between the reference input49 and the sensor input 47 or the reference input 51 and the sensorinput 48 there exists a pressure difference corresponding with theoperating pressure P.

The inlet valve 18 and the outlet valve 21 are in the illustratedexemplary embodiment designed as disk-seat valves. Valves 18 and 21 areeach controlled by a double-acting hydraulic cylinder 52 and 53,respectively, which operate in a push-pull mode. The simultaneousoperation of the valves being such that the inlet valve 18 is in itsblocking position while the outlet valve 21 is open and valve 21 ischanged over into its blocking position, while the inlet valve 18 isopen. Within control circuit 29 there is provided an operating controlvalve 54 which is set by the end-position pressure impulses of theend-impulse transmitters 44 and 46.

This operating control valve 54 is designed as a 4/2-way valve, throughthe changeover of which between its alternative through-flow positions Iand II the control connections 56 and 57 of the control circuit can bechanged alternatively to control-pressure level P_(x) or tank level.According to the illustration, FIG. 1, when control valve 54 is inposition I, upper control connection 56 is connected through a firstcontrol line 58 to the bottom-side control chamber 59 of thedifferential cylinder 52. The pressurized fluid then flows from tank 32,through valve, 54, connection 56 and control line 58 into thedifferential cylinder which results in the pressure loading of inletvalve 18 until valve 18 reaches its closing position blocking off thestorage container 19 against the feed chamber 17. The pressurized fluidalso flows through a control-line branch 58' that extends from the firstcontrol line 58 to the rod-side control chamber 61 of the differentialcylinder 53 provided for operating the outlet valve 21. This fluid flowresults in the pressure loading of which the outlet valve 21 so thatvalve 21 reaches its open position connecting the feed chamber 17 to thefeed line 22.

The second control connection, control connection 57, regulated bycontrol valve 54 of the control circuit 29 is connected through a secondcontrol line 62 to the rod-side control chamber 63 of the differentialcylinder 52. This connection is provided for pressure loading of whichthe inlet valve 18 so that the valve reaches its open positionconnecting the storage container 19 to the feed chamber 17. The fluidsupplied through second control line 62 is also applied through achangeover control device identified in its entirety by the referencenumeral 64 to the bottom-side control chamber 66 of the differentialcylinder 53. This fluid is provided for operating the outlet valve 21,through the pressure loading with control pressure P_(x) so that theoutlet valve 21 reaches its closed position blocking the feed chamber 17of the feed cylinder 11 from the feed line 22.

The changeover control device 64, which will be discussed in greaterdetail hereinafter, has the function that indeed the pressure connectioninto the bottom-side control chamber 66 of the drive differentialcylinder 53 of the outlet valve 21 occurs simultaneously with thepressure connection into the rod-side control chamber 63 of the drivedifferential cylinder 52 of the inlet valve 18. Consequently, when thepump 10 works in the feed operation, that is, the material flow isguided pulsatingly from the storage container 19 to the feed line 22,the outlet valve 21 opens only when a pressure corresponding at leastapproximately with the pressure existing in the feed line 22 is built upin the feed chamber 17.

The settings of the main slide valve 38, which controls the movement ofthe drive cylinder 12, are based on the end-position pressure impulsesof end-position pressure-impulse transmitters 67 and 68 which are,respectively, attached to the top and bottom ends of differentialcylinder 52. End position transmitters 67 and 68 are analogous in designand function to the end-position impulse transmitters 44 and 46 of thedrive cylinder 12. More specifically, both transmitters 67 and 68monitor the changeover of piston 69, transmitter 67 being associatedwith rod side control chamber 63 and transmitter 68 be associated withthe bottom side control chamber 59. When pump 10 is in operation, mainslide member 38 during the feeding operation is switched into itsoperating position I by an output impulse of the end-position impulsetransmitter 67. The transmission of an pulse by transmitter 67 occurswhen the inlet valve 18 reaches its blocking position. Specifically,main slide valve 38 is set in position I by the pressure loading itsfirst control chamber 39 in response to valve 18 reaching its blocking,or closed position. Once slide valve 38 is set in position I, thepressurized fluid accumulated at the operating-pressure supplyconnection 26 is connected into the bottom-side driving pressure chamber23 of the drive cylinder 12. When slide valve 38 is set in thisposition, the rod-side pressure chamber 24 of drive cylinder 12 issimultaneously connected to the tank 32 of the pressure-supply plant sothat the pistons 13 and 16 of the drive cylinder 12 and of the feedcylinder 11 are displaced in feeding direction 41. Main slide switch 38is switched to operating position II in response to an output impulsefrom the second end-position impulse transmitter 68 of the differentialcylinder 52. This pulse occurs as a result of the changeover of theinlet valve 18 during the feeding operation of the pump 10. When mainslide valve 38 is set in position II, the bottom-side driving pressurechamber 23 of the drive cylinder 12 is relieved of pressure toward thetank 32 of the pressure-supply plant 28. Simultaneously, the rod-sidedriving pressure chamber 24 of the drive cylinder 12 is loaded with thefluid charge to the operating pressure P. Collectively, these actionscause the pistons 13 and 16 of the drive cylinder 12 and of the feedcylinder 11 to be displaced in the direction of arrow 43 associated witha loading phase of the feed chamber 17.

The inlet valve 18 is open and the outlet valve 21 is closed during thisphase of movement of the feed-cylinder piston 16.

To discuss the function of the viscous fluid pump 10 and its controldevice in greater detail, an initial situation corresponding with thefeeding operation will now be described. In this situation, the piston16 of the feed cylinder 11 carries out a feeding stroke, that is thepiston 13 of the drive cylinder 12 is loaded on the bottom side withfluid charged to the operating pressure P from the adjustable throttle37 through the main slide valve 38, which is in its operating positionI. (The valve 38 was switched earlier into this operating position I bythe end-position pressure impulse produced by the end-position impulsetransmitter 67 upon reaching the closing position of the inlet valve18.) When the pump 10 is in this state, the rod-side driving pressurechamber 24 of the drive cylinder is relieved of pressure, the inletvalve 18 assumes its blocking position shown in full lines and theoutlet valve 21 assumes its open position shown in full lines. Thecontrol-pressure loading of the bottom-side control chamber 59 needed inthis respect and the relief of pressure of the rod-side control chamber63 of the operating cylinder 52 of the inlet valve and thecontrol-pressure loading of the rod-side control chamber 61 and pressurerelief of the bottom-side control chamber 66 of the changeover cylinder53 of the outlet valve had thereby been achieved by the changeover ofthe operating control valve 54 into its operating position I, whichchangeover occurred during passage through the bottom side end positionof the drive-cylinder piston 13 and was triggered by the output impulseof the end-position impulse transmitter 46.

From its initial position corresponding to the illustration of FIG. 1,the piston 13 of the drive cylinder 12 moves towards its end position onthe side of the feed cylinder. Shortly before piston 13 reaches its endposition, the first end-position impulse transmitter 44 produces achangeover impulse which is transmitted to the operating control valve54. Valve 54 which is in position I, is then switched into its operatingposition II. When valve 54 is in this position, the control pressureP_(x) now becomes present at the control connection 57 and the controlconnection 56 of the control circuit 29 is relieved of pressure towardthe tank 32. Thus, while the drive-cylinder piston 13 continues to movetoward its end position on the side of the feed cylinder, the rod-sidecontrol chamber 63 of the changeover cylinder 52 of the inlet valve 18is charged with pressurized fluid through the second control line 62 andthe bottom-side control chamber 66 of the changeover cylinder 53 of theoutlet valve 21 is loaded through the changeover control device 64 withfluid pressurized to control pressure P_(x). At the same time, thebottom side control chamber 59 of the changeover cylinder 52 of theinlet valve 18 and the rod-side control chamber 61 of the changeovercylinder 53 of the outlet valve 21 are relieved of pressure through thefirst control line 58, causing the inlet valve 18 to open and the outletvalve 21 to close. Consequently, these changeover operations of theinlet and outlet valves occurring very quickly.

When piston 69 reaches its end position, which corresponds to reachingthe maximum opening cross section of the inlet valve 18, an end-positionoutlet impulse from the bottom-side end-position impulse transmitter 68is produced. This impulse is transmitted to through which the main slidevalve 38 so as to cause valve 38 to switch into its operating positionII. When the main slide valve is in this position, the bottom-sidedriving pressure chamber 23 of the drive cylinder 12 is relieved ofpressure and its rod-side driving pressure chamber 24 is charged withfluid at the operating pressure P. The feed-cylinder piston 16 carriesout now its loading stroke occurring in direction of the arrow 43,during which goods to be transported flows from the storage container 19into the enlarging feed chamber 17 because the closed outlet valve 21 isblocked off from the feed line 22.

With the piston 13 of the drive cylinder 12 approaches its bottom-sideend position, that is, directly before it reaches this end position, thesecond end-position impulse transmitter 46 of the drive cylinder 12produces an output impulse. This impulse is applied to operating controlvalve 54 so as to cause the valve to return to its operating position I.Consequently, high control pressure P_(x) fluid becomes present again atthe control connection 56 and reaches through the first control line 58against the bottom-side control chamber 59 of the changeover cylinder ofthe inlet valve 18 and, through the control-line path 58', the rod-sidecontrol chamber 61 of the changeover cylinder 53 of the outlet valve 21.Since the rod-side control chamber 63 of the changeover cylinder 52 isconnected through the second control line 62 and the operating controlvalve 54 again directly to the--pressureless--tank 32 the inlet valve 18immediately transfers again into its closing position blocking off thestorage container 19 from the feed chamber 17. Upon reaching the closingposition, the rod-side end-position impulse transmitter 67 produces apressure outlet impulse, through which the main slide valve 38 is againswitched into the operating position I associated with the feedingoperation of the drive cylinder 13, thus starting the feeding stroke ofthe piston 16 of the feed cylinder 11, which feeding stroke occurs indirection of the arrow 41.

In contrast to the inlet valve 18, which, practically simultaneouslywith the switching of the operating control valve 54 into its operatingposition I, reaches its blocking position, the opening of the outletvalve 21 is delayed. This occurs because of the action of the changeovercontrol device 64, until the operating pressure in the bottom-sidedriving pressure chamber 23 of the drive cylinder 12 and thus also thepressure in the feed chamber 17 reaches a minimum value and pressuremedium can only thereafter flow from the bottom-side control chamber 66of the changeover cylinder 53 of the outlet valve 21 toward the tank 28.

The changeover control device 64 of the illustrated version of theinvention includes a pressure valve 71, which is urged by a valve spring72 with an adjustable initial tension into its blocking position. Valve71 is loaded in its opening direction by the operating pressure Pbuilding up in the bottom-side driving pressure chamber 23 of the drivecylinder 12 during the feeding operation. The fluid charged to pressureP is supplied to valve 71 from a pickup point 79 between the main slidevalve 38 and the drive cylinder 12. Changeover control device 64 furtherincludes a check valve 73 connected in parallel with the pressure valve71, with this parallel connection existing between a bottom-sideconnection of the changeover cylinder 53 of the outlet valve 21 and thesecond control line 62. The check valve 73 being poled through arelatively higher pressure in the bottom-side control chamber 66 of thechangeover cylinder 53 of the outlet valve 21 in blocking direction andthrough a relatively higher pressure in the second control line 62 inpassing direction. The pressure utilized for the open-control of thepressure valve 71 can also be picked up directly at the outlet 34 of thehigh-pressure pump 36, or also "somewhere" between said valve and thedrive cylinder 12 or at another pressure line connected to thebottom-side driving pressure chamber of the drive cylinder 12.

By adjusting the initial tension of the valve spring 72, it is possibleto adjust the "opening pressure" at which the pressure valve 71 reachesits open position. An advantageous adjustment is thereby that thepressure valve 71 opens when the pressure P₁ building up in the feedchamber 17 at the start of the feeding stroke of the piston 16 of thefeed cylinder 11 has the same or approximately the same value as thepressure P₂ existing in the feed line 22. When this relationship isreached by adjusting the initial tension of the valve spring 72, then anoptimum quiet pump operation is achieved since then, when the outletvalve 21 opens, no return flow from the feed line 22 into the feedchamber 17 or a sudden relaxation of the same toward the feed line 22occurs, which would be linked to an undesired noise development and alsowear-promoting vibrations of the pump 10.

In place of the pressure valve 71 freeing an increasing opening crosssection with an increasing operating pressure P after exceeding theminimum opening pressure and of the check valve 73 connected in parallelthereto, an alternative changeover device 64' is shown in the detailedillustration of FIG. 1a. Changeover device 64' includes apressure-remote-controlled check valve 73', which combines the functionof the check valve 73 and of the pressure valve 71 of the changeovercontrol device 64 of FIG. 1 in one structural element valve 73' however,has a different--"step-like"--changeover characteristic compared withthe changeover control device 64 due to the fact that as soon as itopens, the valve 73' assumes immediately an open state with a maximumopening cross section.

To influence the opening behavior of the outlet valve 21, a pressurereducer 74 is also suited with which, in a definite, if necessaryadjustably changeable reducing ratio i_(min) in relation to theoperating pressure P, which exists in the bottom-side driving pressurechamber 23 of the drive cylinder 12, or to the pressure P₁ which buildsup in the feed chamber 17 during a feed phase of one pump cycle.Pressure reducer 74 is employed to adjust the pressure P₃ to support theopening of the outlet valve 21 into the rod-side control chamber 61 ofthe changeover cylinder 53 of the outlet valve 21. The pressure reducer74 is connected to the first control line 58 through a control-line path58'.

In place of the end-position impulse transmitter 68, which is associatedwith the inlet 18 and which, when the piston 69 of the changeovercylinder 52 of the inlet valve 18 reaches its bottom-side end position,produces an impulse to change over the main slide valve 38, it ispossible to utilize, as shown in dashed lines, an end-position impulsetransmitter 68' associated with the outlet valve 21, which produces anoutlet impulse. The pulse generated by end-position transmitter 68' canbe used to initiate the changeover of the main slide member 38 when theoutlet valve 21 reaches its closing position, which would have to takeplace like the hydraulic control of the changeover cylinders 53 and 52of the outlet valve 21 and of the inlet valve 18 as a rulesimultaneously with reaching the open position of the inlet valve 18.Since, however, attaining the closed position of the outlet valve 21 canbe slightly delayed compared with attaining the open position of theinlet valve 18, it is particularly advantageous to utilize the outletimpulse of the end-position impulse transmitter 68' which outlet impulseis characteristic for attaining the closed position of the outlet valve21, to change over the main slide member 38 so that it is assured duringthe course of the sequence control that the main slide valve 38 does notchange over until the outlet valve 21 has reached this closed position.

In order to be able to also use the viscous fluid pump 10 when necessaryin a return operating mode, in which goods to be transported is pumpedfrom the feed line 22 back into the storage container 19, a firstoperational changeover valve 76 is provided. Valve 76 is connectedbetween the operating control valve 54 and the two control lines 58 and62. A second operational changeover valve 77, through which the outletimpulses of the end-position impulse transmitters 67 and 68 or 68' canbe fed to the control chambers 39 and 42 of the main slide valve 38 isalso provided to facilitate reverse or reverse operation of the pump.

The operational changeover valves 76 and 77 are designed as 4/2-wayvalves and have spring-centered base positions O associated with thefeeding operation. Through a common, electrical or manualoperation,valves 76 and 77 are switched to "activated" operatingpositions I, in which the changeover operations of the inlet valve 18and of the outlet valve 21 are synchronized with the operating strokesof the drive cylinder 12 and of the feed cylinder 11 such that the goodsto be transported is returned from the return line 22 into the storagecontainer 19.

The high-pressure pump 36 of the pressure-supply plant 28, whichhigh-pressure pump is a control pump, has an only schematicallyindicated control member 78. Control member 78, the design and functionof which is known, performs a load-sensing operation of thehigh-pressure pump 36 so that during the operation of the viscous fluidpump, the hydraulic oil volume stream flowing through the throttle 37 istimely constant, which corresponds with a control of the viscous fluidpump 10 to a constant material flow during the feeding and loadingphases of the pump cycles. This control takes place in dependency of therespective operating pressure, which is picked up in the direct vicinityof the driving pressure chambers at pickup points 79 and 81 and is fedthrough a changeover check valve 82 and a control valve 83 to thecontrol member 78. This control valve 83 is in the illustrated exemplaryembodiment designed as a pressure-controlled 3/2-way valve, thespring-centered base position O of which is a through-flow position, inwhich the operating pressures guided through the changeover check valve82 to the control valve 83 are forwarded to the control member 78.

Through the end-position output impulses of the end-position pressureimpulse transmitters 44 and 46 of the drive cylinder 12, which through afurther changeover check valve 84 are guided to the control chamber 86of the control valve 83, the valve is changed during the movementchangeover operations of the drive cylinder 12 to its operating positionI. When control valve 83 is in operating position I, the maximum controlpressure P_(x) is active at the control member 78 so that in thesemovement reversing phases the control pump 36 operates with a maximumfeed performance.

The switching arrangement of the first operational changeover valve 76"between" the operating control valve 54 and the control connections 56of the control system 29, shown in full lines, is equivalent in functionto a switching arrangement of this valve 76 "between" the end-positionimpulse transmitters 44 and 46 of the drive cylinder 12 and theoperating control valve 54, shown in dashed lines When changeover valve76 is so repositioned, the base position of the valve 76 is such thatthe end-position signal outlet 50 of the first end-position impulsetransmitter 44 is connected to the control chamber 87, through thepressure loading of which the operating control valve 54 is switchedinto its operating position II. The impulse outlet 55 is connected tothe control chamber 88 of the operating control valve 54, through thepressure loading of which control chamber the operating control valve 54is switched into its operating position I.

The hydraulic switching arrangement including the main slide valve 38,the operating control valve 54, the operational changeover valves 76 and77, the two changeover check valves 82 and 84 and the pump control valve83 are combined in a particularly advantageous design to form onehydraulic block identified in its entirety by the reference numeral 90.Hydraulic block 90 can be utilized with the design discussed in detailin connection with FIG. 1 also for the pressure supply and valve controlfor a two-cylinder viscous fluid pump. Such pump, for example, caninclude two pumps of the type described in connection with FIG. 1operating in a push-pull manner. The feed lines 22 of the individualpumps start out from the feed chambers 17, end in a so-called "Y-pipearrangement" in one single, not illustrated, extended feed line, inwhich the stream of material flows essentially continuously.

Such a pump 10' is represented in FIG. 2, includes two drive cylinders12 and associated feed cylinders 11. Each feed cylinder 11 has an inletvalve and an outlet valve and a changeover control device, the detailsof which will now be discussed. For reasons of simplicity, pump 10' isdescribed as having two drive cylinders 12/1 and 12/2, two double-actingdifferential cylinders 52/1 and 52/2 that control the inlet valves intoand out of each of the feed chambers 11, two differential cylinders 53/1and 53/2 for controlling the opening and closing movements of the feedchamber outlet valves and two changeover control devices 64/1 and 64/2.

As far as the same reference numerals are used for parts of FIGS. 1 and2, this makes reference to structural and functional equality and/oranalogy and at the same time refer to the above description portionrelating thereto.

The bottom-side driving pressure chambers 23/1 and 23/2 of the two drivecylinders 12/1 and 12/2 are attached to the individual outlet ends ofmain slide valve 38 through outlet connections 79 and 81, respectively,of the hydraulic block 90. The outlet connections 81 and 79 also formthe pickup points, where by means of the changeover check valve 82 therespective operating pressure is picked up and is fed to the controlmember 78 of the control pump 36. The two rod-side driving pressurechambers 24/1 and 24/2 of the two drive cylinders 12/1 and 12/2 are inconstant communication with one another through a crossline 91. In afunctionally equivalent design of the viscous fluid pump 10' in place ofthe bottom-side driving pressure chambers 23/1 and 23/2 of the drivecylinders 12/1 and 12/2, their rod-side driving pressure chambers 24/1and 24/2 could be connected to the outlet connections 81 or 79 of thehydraulic motor 90 and instead their bottom-side driving pressurechambers 23/1 and 23/2 could be connected to one another through a"rocker oil line" corresponding in function with the crossline 91.

Viewed in the common feeding direction 41 of the drive cylinders 12/1and 12/2, which are arranged axially parallel only for the purpose ofthe description, the left drive cylinder 12/2 has pressure-impulsetransmitters corresponding in design and function with the end-positionimpulse transmitters 44 and 46. The signal outlets 55 and 50 of thepressure-impulse transmitters are connected to the correspondinglyidentified connecting points of the hydraulic block 90, from where theend-position outlet impulses are guided through the changeover checkvalve 84 to the control chamber 86 of the control valve 83. Theseimpulses regulate the setting of valve 83 which, in turn, adjusts pump36 for maximum feed performance by regulation of the control member 78.The output impulses of end-position impulse transmitters 44 and 46 aretransmitted through the first operational changeover valve 76 to thecontrol chambers 87 and 88 of the operating control valve 54, areutilized for its changeover. The inlet valves and the outlet valves are,like in the exemplary embodiment according to FIG. 1, constructed insuch a manner that they assume their blocking position when thebottom-side control chambers of their changeover cylinders 52/1 and 52/2or 53/1 and 53/2 are loaded with the high control pressure P_(x) fluidand their rod-side control chambers are relieved of pressure.

Control lines 92 and 93 are connected to control connections 56 and57,respectively, of the hydraulic block 90. These control lineconnections can be reversed by switching the operating control valve 54with respect to the pressure level--control pressure P_(x) or tankpressure level--, through which control lines the inlet and outletvalves can be controlled in the necessary push-pull operation. The firstcontrol line, line 92, is coupled to the outlet port 34 of pump 36 toreceive the high control pressure level P_(x) fluid when control valve54 is in operating position I. When valve 54 is in operating positionII, line 92 is connected to the tank 32 of the pressure-supply plant 28.When valve 54 is in position II, tank 32 is directly connected to therod-side control chamber 63/2 of the changeover cylinder 52/2 of theinlet valve of the "left" feed cylinder of the viscous fluid pump 10'and to the bottom-side control chamber 59/1 of the changeover cylinder52/1 of the "right" feed cylinder of the pump 10'. When control valve 54is in position II, pump 32 is also hydraulically connected through thechangeover control device 64/2 to the bottom-side control chamber 66/2of the changeover cylinder 53/2 of the outlet valve of the "left" feedcylinder.

The second control line, line 93, the line connected to control outlet57 is directly connected to the bottom-side control chamber 59/2 of thechangeover cylinder 52/2 of the inlet valve of the left feed cylinderand to the rod-side feed chamber 63/1 of the changeover cylinder 52/1 ofthe inlet valve of the right feed cylinder. Control line 93 is alsohydraulically connected through the changeover control device 64/1 tothe bottom-side control chamber 66/1 of the outlet valve of the rightfeed cylinder. The connections of the changeover control devices 64/1and 64/2 on the side of the control line are identified by the referencenumerals 89/1 and 89/2, their connections on the side of the controlchamber by the reference numerals 95/1 and 95/2.

The rod-side control chambers 61/1 and 61/2 of the two changeovercylinders 53/1 and 53/2 are connected to the tank 32 of thepressure-supply plant 28 through individual changeover valves 94 and 96,respectively. When the valves 94 and 96 are in their base positions,position O, which is associated with the normal feeding operation of theviscous fluid pump 10', control chambers 61/1 and 61/2 are connected tothe tank 32.

The inlet valve changeover cylinders 52/1 and 52/2 are each providedwith a "rod-side" end-position-(pressure) impulse transmitter 67/1 or67/2, which correspond with the end-position impulse transmitters 67 and68 of the exemplary embodiment according to FIG. 1. Impulse transmitters67/1 and 67/2 each emit a pressure-output impulse each time when theassociated pistons of the changeover cylinders 52/1 or 52/2 reach theirend position corresponding with the closed position of the respectiveinlet valve.

The pressure-output impulses of the end-position impulse transmitters67/1 and 67/2, are guided alternatingly to the control chambers 39 and42 by the second operational changeover valve 77. When valve 77 is inits base position, position O, during the feeding operation of the pump10' it is switched in each case into such an operating position I or IIso that the feed cylinder associated with the inlet valve 18 which is inthe blocking position will urge to goods to be transported from thestorage container into the associated feed line.

The signal outlets 55 and 50 of the end-position impulse transmitters 44and 46 are connected through the first operational changeover valve 76to the control chambers 87 and 88 of control valve 54 in the switchingarrangement illustrated in FIG. 2.

When the pump 10' is supposed to operated in the return mode, in whichgoods to be transported is pumped from the feed line back into thestorage container, the changeover valves 76 and 77 associated with theoperating control valve 54 and the main slide valve 38 and changeovervalves 95 and 96 associated with the outlet valves are switched from theillustrated base positions O to their alternative operating positions I.This switching can be done manually or be electrically controlled andshould be done in such a manner that all operational control valves 76,77, 94 and 96 are simultaneously switched.

In contrast to the feeding operation of the pump 10', during which theoutlet valve rod-side control chambers 61/1 and 61/2 of the changeovercylinders 53/1 and 53/2 are connected to the tank 32 of thepressure-supply plant 28 through changeover valves 94 and 96, thechambers 61/1 and 61/2 are sequentially loaded during the return modeoperation of the pump 10'. Specifically changeover valves 94 and 96 arereset so that rod-side control chambers 61/1 and 61/2 are alternatingconnected through the control lines 92 and 93 with the high controlpressure P_(x) fluid. In other words, the associated outlet valves are"actively" set into their open positions.

The switching of the outlet valves 21 into their blocking operatingpositions is done like during the feeding operation of the pump 10'.Specifically outlet valves 21 are set by the pressure loading of theirbottom-side control chambers 66/1 and 66/2 through the changeovercontrol devices 64/1 and 64/2 synchronously with the changeover of theinlet valves and in such a sequence that results in the reversal of thestream of material to be transported.

In order to assure that in the return-operation mode the main slidevalve 38 is switched only after the inlet and outlet valves have reachedtheir switched positions suited for reversed material-flow, theimpulse-signal lines 99 and 101, which lead through control connections97 and 98 and changeover valve 108 to main slide valve control chambers39 and 42 are provided with adjustable throttles 102 and 103. Bysuitably adjusting the throttles 102 and 103, a delay in the changeoverof the main slide valve 38 is achieved compared with the changeover ofthe inlet and outlet valves. This is of a particular importance for thereturn-operation mode, during which the outlet valves must beopened--alternatingly--against the material pressure accumulated in thefeeding line, however, the opening of the outlet valves is not supportedby the feeding operation of the feed cylinders.

Alternatively, or in addition to the adjustable throttles 102 and 103,it is also possible to provide the through-flow channels 104 and 106 ofwith the second operational changeover valve 77. The through-flowchannels 104 and 106 are utilized during the reversing operation, withthrottles 107 or 108, which then, however, can only be realized in asimple manner as fixed throttles.

Adjustable throttles 102 and 103 or fixed throttles 107 and 108 withthis function can also be provided in the exemplary embodiment accordingto FIG. 1.

To discuss yet a further exemplary embodiment, reference is now made toFIG. 3 which shows a viscous fluid pump 10". Pump 10" is constructed asa two-cylinder pump and is identical to the exemplary embodimentaccording to FIG. 2 regarding the control of the drive cylinders 12/1and 12/2 and their push-pull control using the hydraulic block 90. Pump10" differs from pump 10' in that for the periodically alternatingconnection of the feed chambers, (not illustrated,) to a common feedline 22, a tube switch 111, namely, a swingable S-tube 112, is provided.Tube 112 is permanently connected to the feed line 22 and is connectedin one of its two swivelled positions communicatingly with the feedchamber of the one feed cylinder, whereas the feed chamber of the otherfeed cylinder is connected to the storage container, and is connected inthe other swivelled end position to the feed chamber of this feedcylinder.

Two changeover cylinders 113/1 and 113/2 acting in opposite directionare provided as the swivel drive for the tube switch 111. The pistons ofcylinders cylinders 113/1 and 113/2 are positively flexibly connected tothe S-tube 112 so that during alternating pressure loading and pressurerelief of their drive chambers 114/1 and 114/2, respectively, work likea single double-acting hydraulic cylinder. The kinematic coupling of thetube switching changeover cylinders 113/1 and 113/2 to the S-tube 112 issuch that the feed chamber of the left feed cylinder is connectedthrough the S-tube 112 to the feed line 22 when the drive chamber 114/2of the left changeover cylinder 113/2 is loaded with high pressure andthe drive chamber 114/1 of the right changeover cylinder 113/1 isrelieved of pressure and vice versa.

The changeover control of the changeover cylinders 113/1 and 113/2 ofthe tube switch 111 takes place analogously to the control of thechangeover cylinders 52/1 and 52/2 of the inlet valves of the exemplaryembodiment according to FIG. 2, with the hydraulic control block 90,discussed in connection with this exemplary embodiment and having theidentical design and the same function, being utilized here with respectto the control of the changeover cylinders 113/1 and 113/2 also in theexemplary embodiment according to FIG. 3.

In as far as the operating elements of FIGS. 1, 2 and 3 have the samereference numerals, this is also supposed to indicate the reference tosameness in design and function or analogy of such elements and thereference to the respective above-disclosed description parts.

The changeover cylinders 113/1 and 113/2 have pressure outputs 117/1 and117/2 functionally corresponding with the end-position impulsetransmitters 67/1 and 67/2 which emit output signals when each timetheir associated pistons reach their end positions. Pressure outputs117/1 and 117/2 are remote from the bottom, toward the respective drivechambers 114/1 and 114/2. Outlets 117/1 and 117/2 thus emit pressuresignals at the level of the control pressure couplable into the drivingchambers 114/1 and 114/2 that are forwarded to the main slide valve 38to switched the valve 38 between its alternative operating positions Iand II.

The feed line 22 can be blocked off from the S-tube for the duration ofthe tube-switch changeover operation by means of a shutoff device 121designed analogously with respect to the outlet valve 21 according toFIG. 1. A differential cylinder 118 is provided for driving the shutoffdevice 121. Differential cylinder 118 has an end-position impulsetransmitter 119 which emits its output pressure impulse when the shutoffdevice 121, after the pressure loading of the bottom-side controlchamber 122 of the differential cylinder 118 with the control pressureP_(x), fluid reaches its end position blocking off the S-tube 112 fromthe feed line 22.

For the operatively correct control of the differential cylinder 118 ofshutoff device 121, there are provided a closing control valve 123, anopening control valve 124, and two operational changeover valves 126 and127. Valves 126 and 127 are designed as 4/2-way valves withspring-centered base positions O in which the valves are positionedduring normal feeding operation. Valves 126 and 127 also have operatingpositions I in which they are set during the return operation of theviscous fluid pump 10". A pressure-controlled supply control valve 128,for controlling the flow of fluid to the tube-switch drives 113/1,113/2, is also provided. Valve 128 establishes a connection to the tubeswitch drives 113/1 and 113/2 only when and as long as the end-positionpressure impulse of the end-position impulse transmitter 119 of thedifferential cylinder of the shutoff device 121 brings about aconnection of the high-pressure outlet port 34 of the pump 36 with thecontrol-pressure connection 33 so that through this the time span isdefined within which the tube switch 111 is switched. The high-pressurepump 36 is also adjusted within this time span through the control valve83 to a maximum feed performance. An additional operational changeovervalve, which can be switched manually or electrically controlled, is2/2-way valve 128' which is connected hydraulically in parallel with thesupply control valve 128. is provided, which valve 128' has a blockingposition I associated with the feeding operation and a through-flowposition II associated with the return operation in which the pressureoutlet port 34 of the high-pressure pump 36 is connected to the controlconnection 33 of the hydraulic block 90. Operationally equivalent withthis would be the insertion of such a 2/2-way valve between thehigh-pressure outlet port 34 of the pump 36 and the control chamber ofthe supply control valve 128.

The functional coordination of these valves provided in addition to theexemplary embodiment according to FIG. 3 will be discussed in detailhereinafter in connection with one operating cycle of the viscous fluidpump 10".

A situation is assumed, in which the "right" feed cylinder of theviscous fluid pump 10" carries out its feeding stroke and the piston13/1 of its drive cylinder 12/1 moves to the "right" in direction of thearrow 41. The driving chamber 114/1 of the right changeover cylinder113/1 of the tube switch 111 is, in this situation, loaded withpressurized fluid. The feeding chamber of the right feed cylinder isconnected through the S-tube 112 of the tube switch 111 to the feed line22. The shutoff device 121 is open, that is, the bottom-side drivingchamber 122 of the differential cylinder 118 of the shutoff device 121is relieved toward the tank 32 of the pressure-supply plant 28 throughthe changeover control device 64 or 64' connected to the drive chamber122. The control line 129 is connected to the changeover control device64 or 64' and the opening control valve 124 and the closing controlvalve 123 are in their illustrated operating positions.

This situation was preceded by the transmission of the end-positionsignal at the pressure outlet 117/1 of the right changeover cylinder113/1. This signal is transmitted to the opening control valve 124 tocause valve 124 to switch to its illustrated operating position I, whichcorresponds with the "parallel" course of its through-flow channels. Thesignal from outlet 117/1 was also transmitted to the main slide valve 38so as to have caused it to switch into its operating position II, whichcorresponds with the "crossed" extent of its through-flow channels. Thesituation was also preceded by the transmission of the end-positionimpulse of the end-position impulse transmitter 44 reacting to the endof the feeding stroke of the left drive cylinder 12/2 of the viscousfluid pump 10". The impulse from the end-position impulse transmitter 44was applied to the closing control valve 123 switch into its illustratedoperating position II, which corresponds with the "crossed" extent ofits control channels in the circuit symbol. The output impulses fromtransmitter 44 was also applied to operating control valve 54 to switchthe valve 54 into its operating position I, which corresponds with the"parallel" extent of its through-flow channels in the circuit symbol.The consequence of these valve operating positions is the assumedinitial situation, in which the right feed cylinder carries out itsfeeding stroke and the left feed cylinder its loading stroke.

During the course of the feeding phase of the right feed cylinder, whichis the loading phase of the left feed cylinder, the piston of the drivecylinder 12/2 of the left feed cylinder reaches its end position nearthe bottom. This causes the end-position impulse transmitter 46 to emita pressure-output impulse. This impulse is transmitted to operatingcontrol valve 54 to cause valve 54 to switch into its operating positionII, which in the circuit symbol corresponds with the crossed extent ofthe through-flow paths. The impulse from transmitter 46 is also appliedto the closing control valve 123 to cause valve 123 to switch into itsoperating position I, which in the circuit symbol corresponds with theparallel extent of its through-flow paths.

The first consequence of this is that the shutoff device 121 reaches itsblocking position since the control line 129, which is loaded with ahigh control pressure fluid, is coupled through the changeover controldevice 64 or 64' into the bottom-side driving chamber 122 of thedifferential cylinder 118 of the shutoff device 121. The consequence ofthis is in turn that with the shutoff device 121 moves into its blockingposition. This movement, in turn, causes the end-position impulsetransmitter 119 of the differential cylinder 118 of the shutoff device121 to produce its pressure-output impulse characteristic for theclosing position of the shutoff device 121. The impulse from transmitter119 is applied to supply control valve 128 to cause valve 128 to switchinto its operating position II corresponding to the crossed extent ofits through-flow paths in the circuit symbol. When valve 128 is inoperating position II, the high control pressure P_(x) fluid becomespresent at the operating control valve 54, which is in operatingposition II. Since valve 54 is in position II, the high pressure fluidis applied to the driving chamber 114/2 of the left changeover cylinder113/2 of the tube switch 111. This causes switch 111 to switch theposition of its S-tube 122 so that it connectes the feed chamber of theleft feed cylinder to the feedline 22. Once this changeover occurs, apressure-outlet signal is emitted at the pressure outlet 117/2 of theleft changeover cylinder 113/2 of the tube switch. This pressure-outletsignal switches the opening control valve 124 into the operatingposition II corresponding in the circuit symbol to the crossed extent ofits through-flow paths. At the same, the signal from outlet 117/2switches the main slide valve 38 into its operating position Icorresponding in the circuit symbol to the parallel extent of itsthrough-flow paths. By switching the opening control valve 124, thedriving chamber 122 of the differential cylinder 118 of the shutoffdevice 121 is again relieved of pressure so that the shutoff device 121can open again. The operating pressure P is coupled through the mainslide valve 38, which is in operating position I, into the bottom-sidedriving chamber 23/2 of the left drive cylinder 12/2 of the viscousfluid pump 10", which causes the left feed cylinder to now operate inthe feeding operation, while the right feed cylinder 12/1 carries outits loading stroke.

The up to now discussed operation is repeated as soon as the piston ofthe drive cylinder 12/2 of the left feed cylinder moves into thevicinity of its end position remote from the bottom and the end-positionpressure-impulse transmitter 44 reacting to this end position emits apressure impulse.

The changeover of the viscous fluid pump 10" according to FIG. 3 to thereturn-operation mode, in which viscous fluid is pumped from the feedline 22 back into the storage container, is done by simultaneouslyswitching the operational changeover valves 76 and 77 or 126 and 127from their spring-centered base positions O, which correspond in each ofthe circuit symbols to the crossed extent of their through-flow paths,into their operating positions I corresponding to the parallel extent oftheir through-flow paths in the circuit symbol, and the operationalchangeover valve 128' designed as a 2/2-way valve into its through-flowposition II. The changeover of the operational changeover valves 126 and127 associated with the tube switch 111 causes, in the return-operationmode of the viscous fluid pump 10", the shutoff device 121 topermanently assume its open position, since operational changeover valve127 actes as a bypass valve in this mode of operation, in the operatingposition I of which valve 127 the closing control valve and the openingcontrol valve are bridged through a bypass path, and the secondoperational changeover valve 126, which is in its operating position Iand associated with the tube switch 111, to keep the rod-side drivingchamber 131 loaded permanently with the high control pressure P_(x)fluid. At the same time, bottom-side control chamber 122 of thedifferential cylinder 118 of the shutoff device 121 is relieved towardthe pressureless tank 32 of the pressure-supply plant and, through theswitching of the 2/2-way valve 128' into its through-flow position II,the pressure supply of the changeover cylinders 113/1 and 113/2 of thetube switch 111 is assured.

In as far as above the end-position impulse transmitters and valvesintended for the sequence control of the feeding and returning operationof the viscous fluid pumps 10, 10' and 10" are designed as hydraulicimpulse transmitters and valves hydraulically controllable by means ofthese impulse, transmitters, it is possible to utilize in their placeand for the same purpose also electrical impulse transmitters andelectrically controllable valves.

We claim:
 1. A hydraulic control device for a viscous fluid pumpcomprising:at least one feed cylinder drivable by means of a hydrauliccylinder, the feed cylinder including a feed chamber that is connectedalternatingly to a storage container through a hydraulically operableinlet valve and to a feed line through a hydraulically operable outletvalve and a feed chamber piston that controls the volume of the feedchamber, the feed chamber piston being coupled to the hydrauliccylinder, the feed cylinder having a loading phase in which the feedchamber piston increases the volume of the feed chamber, the inlet valveis open and the outlet valve is closed, and a feeding phase in which thefeed chamber piston reduces the volume of the feed chamber, the outletvalve is open and the inlet valve is closed; a pump drive connected tothe hydraulic cylinder for controlling the position of the piston in thefeed chamber by selectively applying pressurized fluid to the hydrauliccylinder to actuate the feed chamber piston; and a sequence controllerwhich controls the changeover of the inlet and the outlet valves and thepump drive, the sequence controller including a changeover controldevice acting on the outlet valve, the changeover control device beingconfigured so that after the feed chamber piston performs the feedingphase, the changeover control device holds the outlet valve in itsblocking position until an adjustably preset pressure threshold isreached in the feed chamber the threshold corresponding at leastapproximately with the pressure existing in the feed line, and uponreaching the pressure threshold, the changeover control device sets theoutlet valve into its through-flow position, this changeover beingcaused by valve-controlled pressure relief of an outlet valvecontrol-cylinder pressure chamber, characterized in that the changeovercontrol device which controls the pressure relief of the pressurechamber of the outlet valve control cylinder is designed as anelectrically or hydraulically operable valve controlled by the highpressure produced by the pressure loading of the feed cylinder, thepressure-controlled valve being set so when the pressure in the feedcylinder hydraulic cylinder reaches an adjustably preset minimum valueof pressure, the pressure-controlled valve switches the outlet valveinto the outlet valve through-flow position.
 2. The hydraulic controldevice according to claim 1, characterized in that the control valve isdesigned as a pressure-controlled through-flow valve to which a checkvalve is connected in parallel, the check valve being loaded in anopening direction through higher pressure at its connection remote fromthe outlet valve control cylinder than at its connection to a drivingpressure chamber section of the outlet valve control cylinder.
 3. Thehydraulic control device according to claim 1, characterized in that therelief control valve is designed as a proportional valve with which isconnected in parallel a check valve, the check valve being loaded inopening direction through higher pressure at its connection facing theoutlet valve control cylinder than in the driving pressure chamber ofthe outlet valve control cylinder.
 4. The hydraulic control deviceaccording to claim 1, characterized in that the relief control valve isdesigned as a remote-control check valve which is loaded in a blockingdirection through relatively higher pressure in the driving chamber ofthe outlet valve control cylinder and can be switched through remotecontrol by means of the pressure coupled from the feed cylinder.
 5. Thehydraulic control device according to claim 1, wherein:there is a drivepiston in the feed cylinder hydraulic cylinder connected to the feedchamber piston that drives the feed chamber piston, a main slide valvecontrols the feeding and loading phases of the feed cylinder in that thefeed cylinder hydraulic cylinder has a first end-position indicatorwhich emits a first end-position signal impulse when the drive cylinderpiston reaches the end phase of the feeding stroke in the feed cylinderhydraulic cylinder and a second end-position indicator which emits asecond end-position signal impulse when the drive cylinder pistonreaches the end phase of the loading stroke in the feed cylinderhydraulic cylinder, an operating control valve is provided that isswitched by the end-position signal impulses of the hydraulic cylinderend-position indicators and that operates in a push-pull mode topressure load and pressure relief the inlet chambers of inlet valve andoutlet valve control cylinders in such a manner that the inlet valvecloses when the outlet valve opens and the closing and opening movementsof the inlet valve and outlet valve take place in a reverse sequence, anend-position indicator is provided which produces an output impulse whenthe inlet valve reaches its blocking position, and an end-positionindicator associated with the inlet valve is provided that produces anoutput signal correlated to the widest open position of the inlet valve,and that the outlet signals of the end-position indicators control thechangeover of the main slide valve so as to regulate the feeding andloading phases of the feed cylinder.
 6. The hydraulic control deviceaccording to claim 1, wherein:there is a drive piston in the feedcylinder hydraulic cylinder connected to the feed chamber piston thatdrives the feed chamber piston, a main slide valve controls the feedingand loading phases of the feed cylinder in that the feed cylinderhydraulic cylinder has a first end-position indicator which emits afirst end-position signal impulse when the drive cylinder piston reachesthe end phase of the feeding stroke in the feed cylinder hydrauliccylinder and a second end-position indicator which emits a secondend-position signal impulse when the drive cylinder piston reaches theend phase of the loading stroke in the feed cylinder, an operatingcontrol valve is provided that is switched by the end-position signalimpulses of the hydraulic cylinder end-position indicators that operatesin a push-pull mode to pressure load and pressure relief the inletchambers of the inlet valve and outlet valve control cylinders in such amanner that the inlet valve closes when the outlet valve opens and theclosing and opening movements of the inlet valve and outlet valve takeplace in reverse sequence, an end-position indicator is provided whichproduces an output impulse when the inlet valve reaches its blockingposition and an end-position indicator associated with the outlet valveis provided that produces an output signal when the outlet valve reachesits blocking position, and the signals of the end-position indicatorscontrol the changeover of the main slide valve so as to regulate theleading and loading phases of the feed cylinder.
 7. The hydrauliccontrol device according to claim 1, wherein:the viscous fluid pump isdesigned as a two-cylinder pump, including two feed cylinders, each feedcylinder having a hydraulic cylinder associated therewith, the feedcylinders being driven in push-pull operation controlled by a changeoverof a main slide valve, the feed chambers of the feed cylinders beingconnected through inlet valves to the storage container and throughoutlet valves to the feed line, the push-pull operation of the feedcylinders being communicated through the main slide valve by thepush-pull control of the feed cylinder hydraulic cylinders by means ofcontrol cylinders for controlling the inlet and outlet valves associatedwith each feed cylinder with the operating control of the inlet valvestaking place through the hydraulic differential control cylinderscontrolling the inlet valves through two control lines a first controlline of which is under a high control-pressure level the second of whichis connected to the pump drive, the first and second control lines beingselectively connected to the feed cylinder inlet valves by means of anoperating control valve, with the first control line being connected tothe bottom-side control chamber of a first outlet valve control cylinderand being connected to the rod-side control chamber of a second outletvalve control cylinder and the second control line being connected tothe bottom-side control chamber of the second outlet valve controlchamber and also being connected to the rod-side control chamber of thefirst outlet valve control chamber, a changeover cylinder, characterizedin that outlet signals needed for the reversal of the operating controlvalve are emitted by end-position impulse transmitters which areassociated with one of the feed cylinder hydraulic cylinders providedfor one of the feed cylinders, each end-position pulse transmitteremitting a signal when the piston of the associated hydraulic cylinderreaches its end position connected with the end phase of the feedingstroke or the end phase of the loading stroke, and that the controlsignals needed for the changeover control of the main slide valve areproduced by end-position indicators which are associated with the inletvalve control cylinders, the inlet valve end-position indicators beingconfigured to emit end-position impulses when the pistons of inlet valvecontrol cylinders reach the end position connected with the closedpositions of their respective valves.
 8. The hydraulic control deviceaccording to claim 7 further including an operational changeover devicefor switching the pump to return operation, during which viscous fluidis pumped from the feed line back into the storage container,characterized in that the operational control device is configured toreverse the connections of the first and second control lines to theoutlet valve control chambers.
 9. The hydraulic control device accordingto claim 7, for a two-cylinder viscous fluid pump including:a tubeswitch for the alternating coupling a first feed cylinder in a feedingoperation to a feed line and opening of the other feed cylinder toward astorage container; a third end-position signal indicator for producingoutlet signals as soon as a changeover operation of the tube switchoccurs; a shutoff device for blocking off the feed line during achangeover operation of the tube switch; a closing and opening drive forthe feed line shutoff device, the drive including a differentialcylinder, a piston rod in the differential cylinder for actuating theshutoff device, the piston rod being configured to reach a blockingposition when a bottom-side drive chamber of the differential cylinderis loaded with pressure through the changeover control device andconfigured to reach an open position when the bottom-side drive chamberis relieved of pressure toward the tank source of pressurized fluid; anend-position impulse transmitter for producing an impulse signal whenthe shutoff device has reached its blocking position; and operationalchangeover valves the base position of which are in through-flowpositions associated with the normal feeding operation, and alternativepositions associated with a return operation in which the pump pumpsviscous fluid from the feed line back into the storagecontainer,characterized in that within the sequence controller there isprovided a valve combination including a closing valve and an openingcontrol valve in a hydraulic series arrangement, the valve combinationhaving a first outlet connected to a control inlet of the changeovercontrol device through which the pressure loading of the shutoff devicecontrol chamber occurs for closing the shutoff device, the pressurerelief of the shutoff device control chamber for opening the shutoffdevice also occurring and a second outlet is connected through a firstoperational changeover valve associated with a rod-side control chamberof the differential cylinder of the shutoff device with the pressure atthe two outlets of the valve combination being reversed throughindividual changeover of the closing and opening control valves.
 10. Thehydraulic control device according to claim 9, characterized in that asecond operational changeover valve is provided that is associated withthe shutoff device the operating position of the second operationalchangeover valve being associated with the return operation of the pumpthe high control pressure is permanently present at the firstoperational changeover valve of the shutoff device.
 11. The hydrauliccontrol device according to claim 9, characterized in that thedifferential cylinder provided for the changeover of the shutoff devicehas an end-position indicator which, during the feeding operation of theviscous fluid pump produces outlet signals when the shutoff devicereaches the closed position, the outlet signals controlling a supplycontrol valve through which high pressure fluid is fed to the operatingcontrol valve for controlling the pressure supply of the changeovercylinders of the tube switch, and a changeover control valve is providedthat is connected in parallel with the supply control valve thechangeover control valve being designed as a 2/2-way valve, having abase position associated with the feeding operation of the viscous fluidpump and a blocking position associated with the return operation of thepump wherein, when the changeover control valve is in the returnoperation position, high pressure control fluid is fed to the operatingcontrol valve.
 12. The hydraulic control device according to claim 7,characterized in that end-position impulse signals released with theclosing of the feed cylinder inlet valves are applied to the main slidevalve through time-delay elements.
 13. The hydraulic control deviceaccording to claim 12, characterized in that the main slide valve isdesigned as a pressure-controlled valve, which is switched through analternative pressure loading of two control chambers between twooperating positions, in which each one of the drive cylinders of thepump is loaded with pressure and the other one is relieved of pressure,and the end-position that monitor the state of the inlet valves sendend-position impulses to the main slide valve control chambers when theinlet valves reach their blocking positions to control the state of themain slide valve.
 14. The hydraulic control device according to claim13, characterized in that the impulse-signal paths for the end-positionimpulses to the control chambers of the main slide valve are guidedthrough an operational changeover valve having a base positionassociated with the normal feeding operation, and an alternativeposition of which is associated with a return fluid flow operation ofthe pump.
 15. The hydraulic control device according to claim 13,characterized in that the throttle points of the impulse-signal pathsare formed by adjustable throttles.